This invention is directed to improved releasable fasteners for holding a plurality of sheets together wherein the improved fasteners include locating indicia markings on an activating element of the fastener with the indicia markings being readable against a fixed location on the body of the fasteners to indicate the thickness of the sheets which are connected together by the fasteners.
In many industries, particularly the aircraft industry releasable fasteners are utilized to clamp together several sheets of sheet metal by inserting the fasteners through aligned apertures in the sheet metal. In many assemblies as, for instance, aircraft assemblies, only one side of the work area is accessible to the assembler. Particularly useful for this type of assembly work is a releasable fastener which has a pair of pins each of which has a shoulder.
The pins are moved in and out of the body of the fastener and include a spacer bar positioned between the pins. When the pins are extended from the body of the fastener, the shoulders on the pin extend beyond the end of the spacer bar and are biased together reducing the effective diameter of the shoulders. This allows the pins to be inserted into the aligned apertures of an assembly of metal sheets. The pins are then retracted back into the body of the fastener and as the shoulders pass over the space bar they are moved laterally outward with respect to one another effectively increasing the diameter of the shoulders beyond that of the diameter of the aperture opening. The shoulders engage the back sheet of material and bring it and any intermediate sheets of material toward the front sheet of material which abuts against the body of the fastener.
The above described releasable fasteners are ubiquitously used in sheet metal assembly and are available in many sizes, shapes and forms. Typically these releasable fasteners will be color coded to indicate the size aperture they are to be used with as, for instance 3/32, 1/8, 5/32, 3/16, 5/16 and the like. Irrespective of the diameter of the aperture opening which the fastener is manufactured to fit, the fastener might be utilized to temporarily hold 2, 3, 4 or even more individual sheets, plates or other structures in alignment with one another prior to permanently fastening these components together utilizing rivets or other permanent fasteners as, for instance, blind fasteners.
The rivets or other permanent fasteners which are utilized to permanently hold the finished structure together must be properly sized with respect to the overall thickness of the combined sheets in order to effectively join the sheets or plates in a unified structure. If the rivets or permanent fasteners are too long, they will do their job inefficiently and/or will not tighten properly, and if they are too short they cannot be secured to the sheets or plates to attach them together.
Particularly useful for temporarily attaching two or more sheet metal sheets together is a first type of releasable fastener which utilizes an internal spring to withdraw the shoulders on the pins toward the body of the fastener for securing the fastener to the work sheets. These releasable fasteners are utilized with a pair of special pliers adapted to compress a shaft into the body of the fastener. This compresses the spring and protracts the pins out of the body of the fastener to position the shoulders on the pins beyond the spreader reducing the diameter about the shoulders of the pins. Once the fastener is positioned in the aperture openings of the sheet metal tension on the special pliers is released allowing the bias of the spring to withdraw the pins back into the body to secure the fastener on the metal sheets.
Another widely used fastener utilizes a threaded shaft for retracting the pins back into the body of the fastener to secure the fastener to the assembly. This type of releasable fastener is very useful for attaching heavier stock together which requires greater force as, for instance, in attaching sheets or plates to structure elements. In this type of fastener a nut on the threaded shaft is rotated to axially move the shaft and in doing so retract the pins back into the body of the fastener. Typically this type of fastener is utilized with a torque limiting rotatable driving tool to speed up assembly.
In modern aircraft construction, different thicknesses of sheet metal, plates or structural elements are utilized and a different number of sheets are utilized in a variety of places in the aircraft. Further, sealant is often positioned between the individual sheets to further adhere the sheets to one another in addition to securing of the sheets, plates and structural elements together by rivets, bolts, fasteners and the like.
While in an exposed area, the thickness of the sheets and/or the number of the sheets may be readily apparent to an experienced assembler, in blind areas this is not the case. Typically in a modern aircraft blind areas as, for instance, tail assemblies, wing assemblies and the like constitute a large percentage as, for instance about 30 percent or more, of the aircraft structure.
If an inappropriate sized fastener is applied to an assembly of sheets and only after the fastener is secured is it evident that its size was inappropriate, the fastener must be removed and the properly sized fastener applied. For rivets, blind fasteners and the like this usually requires drilling of the inappropriate fastener from the sheets. Not only is this a labor consuming process, but in a blind area the internal portion of the fastener must also be removed. It can not be allowed to drop into the blind area of the aircraft. It is evident that it would be extremely inappropriate to have loose pieces of rivets or blind fasteners flying around within the internal structure of a high speed aircraft which can undergo many times the force of gravity during turns, banks and the like. Thus, it is very important that the correct sized fastener be utilized to join a plurality of sheet metal sheets, plates or structural assemblies.
Heretofore special scales were utilized to measure the thickness of a plurality of sheets comprising an assembly of sheets. These scales have a stepped surface on one end of a probe on the scale. The probe is pushed through the aperture and stepped surface hooked against the back sheet. The thickness of the sheet is then read against the scale by reading the surface of the top sheet or outside sheet against the scale.
With the increased use of sealants between individual sheets in an assembly of sheets the use of this scaled technique is not accurate unless it is known that the sheets are held in a very tight registry with respect to one another. Measurement of the thickness of an assembly of sheets or plates through an opening may not accurately reflect the thicknesses of the sheets and plates because of bulging or the like by sealant located between the sheets. This necessitates securing the sheets together with one of the above releasable fasteners to compress and spread the sealant and then removing the fastener and measuring the thicknesses of the sheet followed by repositioning of the fastener back in the aperture.
This process is often complicated because the assembly in one portion of the aircraft may span over several shifts of workers. To assure that they are using the proper size fasteners each shift of workers must withdraw the fasteners and measure the thickness of the sheets and then reinsert the fasteners. This is a labor intensive and thus expensive operation.